1. Field of the Invention
The present invention relates to a golf club head including scorelines formed in its face surface, and a method of manufacturing the same.
2. Description of the Related Art
It is a common practice to form scorelines in the face surface of an iron type golf club head by cutting (for example, Japanese Patent Laid-Open Nos. 2010-57679, 2010-131140, and 2010-263975). FIG. 9 shows a method of forming scorelines (FIG. 5 in Japanese Patent Laid-Open No. 2010-57679) using an NC (Numerical Control) cutting machine. A golf club head 1 in which scorelines are to be formed is fixed to the NC cutting machine via a jig 2. The NC cutting machine includes a spindle 4 which is rotated about the Z-axis and has a lower end to which a cutting tool (end mill) 5 is attached.
After plane coordinates are set on the face surface of the golf club head 1, the spindle 4 is rotated to move the golf club head 1 and cutting tool 5 relative to each other in the direction (X-direction) in which scorelines are formed, thereby cutting the face surface so as to form groove-shaped scorelines in it. A large number of scorelines are formed so that they extend in the toe-to-heel direction and are vertically aligned to be parallel to each other.
FIG. 10 illustrates an example of the cross-sectional shape of scorelines 6 as described above (FIG. 4 in Japanese Patent Laid-Open No. 2010-57679). The scoreline 6 has an almost inverted trapezoidal cross-sectional shape and a flat bottom surface. Note that the corner edges at which the side surfaces of the scoreline 6 intersect with the face surface are rounded, and this arrangement complies with the golf rule (the so-called two-circle rule explained in paragraphs 0018 to 0021 of Japanese Patent Laid-Open No. 2010-57679).
To form scorelines 6 having flat bottom surfaces, the face surface is cut using an end mill 7 having a flat-topped surface 7f as its distal end surface, as shown in FIG. 10. More specifically, a hole is drilled in the face surface up to a predetermined depth using the end mill 7 upon pressing of the end mill 7 against the face surface, and then a groove is formed upon movement of the end mill 7 in the X-direction of FIG. 9, thereby forming scorelines 6 in the form of grooves having an equal depth.
In this case, the end mill 7 is tapered narrower to have a flat-topped surface with a small diameter as its distal end surface 7f, so a large load is imposed on the distal end of the end mill 7 upon its pressing against the face surface, and may quickly wear or damage the end mill 7. When the end mill 7 is very slowly pressed against the face surface, the above-mentioned problem can be avoided, but the cutting time is prolonged, thus degrading the productivity.